Eric F

A scratch won't compromise CF unless it is deep enough to damage the integrity of the resin and fiber matrix. Following the installation specs for parts goes a very long way to the longevity of the parts, regardless of material. That said, some are more tolerant than others of hamfistedness.

I have some CF seatposts that are over 20 years old and still doing just fine.

genejockey 

A used carbon seatpost of unknown history, ridden for a time WAY past the minimum insertion by somebody who weighs about 270, and is over 6' tall, in a 47cm bike, then swapped to another bike and then not inserted enough, and possibly tightened down too much more than once because of slipping may be a bad choice for a large guy who rides rough.

rydabent

It looks to me that this is a case of trying to save weight by buying a bike with a way too small of a frame. Then to make up for the small frame, a way too long of a seat post was used.

Atlas Shrugged

Thanks again, Larry, you are indeed an artist at what you do.

For the usual crew who jump onto this excellent thread with the Carbon will be the death of anyone who uses this devils concoction its a bit late now. Carbon has been taking over the sport for the past 20 years or more, and your sky is falling narrative is losing its effect. The "steel is real" crew is like a doomsday cult which keeps missing its end-of-the-world date and preaching just wait, it's coming any day now.

mstateglfr 

He incorrectly installed a component but its not his fault?
um...

mstateglfr 

Of course you do since you are staunchly analog.
I too am staunchly analog, but I recognize its simply preference rather than a dogmatic belief that it is somehow actually better in any instance I can opine on.

I have a carbon seatpost on my gravel bike. I am tall, its a sloping top tube, and there is a ton of seatpost showing. That thing is comfortable as a result. I have absolutely 0 fear of it breaking, relative to the old Easton aluminum seatpost it replaced. If either broke, I would consider it a freak incident instead of using it as a way to further solidify my bias.

Your example of some tri guy is of 0 use here. As a counter I could pull up countless examples of steel frames failing, but that doesnt mean stell is inherently weak, so I wont do something lazy like that.

terrymorse 

One could cite a laundry list of reasons why an aluminum post makes no sense. Stress corrosion cracking, no fatigue limit, weak material, galvanic corrosion, etc.

LarrySellerz

you tend to be good at following my stories. This is almost right except that this seatpost wasn’t slipping. The only clue I have that it was overtightened is that it failed.

My point about the slipping seatpost was suggesting that having a seatpost where overtightening a commonly tightened bolt has a good chance of causing catastrophic failure is a design flaw.

elcruxio

There are quite a few commonly tightened bolts on a bicycle where overtightening can cause catastrophic failure. Without carbon being present.

drlogik 

So far so good but I will stand by my opinion. Yes, other materials can fail also for the reasons I (and others) stated above. They include aluminum, steel and I'm sure titanium as well. And before you call me a carbon basher, I have the utmost confidence in carbon if it is applied in the appropriate manner.

I personally would not put a carbon seat post on my bike. I also would not put a relatively thin-walled aluminum seat post on my bike either. I have personally seen those fail. I'll take a few more pounds off my middle before I try to save a few ounces on my bike.

Many years ago we saw a snapped steel seat post come in on a kids bike. Don't ask me how.... The kid was ok and the dad wasn't walking funny. They said it just "broke". Heck, I managed to strip the crank on the bottom bracket spindle on a Raleigh Super Course back in the day so freak fails do occur.

Carbon has its permanent place in the cycling world, no doubt. I just don't trust it holding my bum up above a potential anal projectile.

Eric F

Not really. Lightweight carbon seatposts are made because there is a demand for them in the market. However, achieving that light weight means that they less resistant to things like over-torqueing of the binder bolt, and random lateral impact forces. It's not a design flaw, it's the side-effect of achieving the design goal. As such, the manufacturers have specific guidelines on how the seatpost is to be installed so as not to damage the structure. If you ignore those guidelines, you have exceeded the design parameters, and failure becomes an increasingly likely result. I own a torque wrench because operating within the manufacturer's safety guidelines matters to my health. Generally speaking, seatposts - like many other things - have 3 factors: 1) Light weight, 2) Low cost, 3) Durability. Pick 2.

tomato coupe

If the bolt was tightened properly, then the seat post wouldn't slip.

Maelochs

WRONG.

Putting a part which has specific limits on a bike sold to someone who cannot understand basic thoughts is a problem ....

Mr. LarrySellerz, I am not trying to tear you up or knock you down, but Please, grow up.

If YOU overtighten a bolt out of Ignorance, don't blame the bolt. Blame the dolt.

Again .... like others here .... I am extremely overweight and have long exposed carbon-fiber seat posts and none of them have ever broken. The two times I have broken CF seat posts were both instances where I knew i was not inserting the post quite enough .... about as much too much as you had exposed. Other than that---see, some folks learn lessons from their mistakes-----I have never had a CF seat post break. The seat post broke because you used it incorrectly.

It is the same situation with your derailleur. If you kick it enough you will bend it and it will never work until you remove it and get everything back in line (don't ask how I know.) You cannot blame the derailleur designer or manufacturer. You deliberately misused and abused the part and damaged it. If you try to hammer a nail with a champagne flute, the subsequent breakage is not due to the bad design or manufacturer of the glass goblet.

Look--you can buy a pistol and if you shoot yourself in the foot, you cannot say that the gun manufacturer didn't make the barrel twelve feet long so you couldn't aim at yourself ...... you are supposed to be a responsible adult taking full responsibility for Your actions.

You are saying that if you tried to cut someone's hair with a chainsaw and cut off somebody's head, you don't blame the chainsaw manufacturer.

YOU messed up. You didn't bother to learn how to use what you bought, and you used it WRONG, and it broke----because YOU BROKE IT.
********************************************
That is really the crux of the issue: Stop Blaming People. Just be honest that you didn't learn how to use the part you bought and broke it. Take Responsibility. That way you will not make similar mistakes down the road.

Really, this isn't that big a deal. You abused a part, it broke, no big deal. I am sure a lot of us have made this error. I know I have, many times. No big deal.

The Big Deal portion of all this is that you step up and accept the consequences of your actions so that you can Not be in this same situation again later.

You can make the bike you showed---the Trek---work for you. Just do it right---a longer CF post, properly tightened, or an Al post.

On the other hand, you could completely mess up the new bike you showed us if you continue to misuse and abuse its component parts.

Your life, your choices.

LarrySellerz

CF seatpost are a bad idea. I’ve tightened dozens of seatposts and never once worried about potentially maiming someone if it’s too tight. There is a time and place for carbon, and as demonstrated by this thread there is good arguments to be made for NOT having it in the seatpost.

LarrySellerz

name 2, and they should be easily overtightened

Eric F

I would agree that CF seatposts are a bad idea FOR YOU. For many other people who follow correct installation protocols, they are not an issue. You've talked about the seatpost bolt being frequently used. Again, maybe that's the case FOR YOU, and another reason why CF is a bad material option FOR YOU. Personally, I have bikes where the seatpost bolt hasn't been touched in years. On my newest bike, I've turned stem and handlebar bolts a LOT more than the seatpost bolt in the past couple of months while trying to fine-tune my fit. Making a blanket claim that CF is a bad choice for seatposts, in all situations, for every user, is just false.

tomato coupe

Why are you worried? You don't own a metric Allen wrench, so there's no chance you could ever over tighten a carbon seat post.

Eric F

Steerer tube bolts. Handlebar bolts. They generally have the same/similar torque specs as seatposts. Overtightening has the same potential issues as a seatpost - eventual failure.

badger1

No. This thread does not contain any "good arguments" against the use of carbon fibre seat posts. None. A good argument advances good reasons, supported by relevant evidence. Both elements are absent here.

All that this thread has demonstrated, to this point, is that using a carbon fibre seat post might be a bad idea for you, and possibly for any third-parties who have installed a carbon fibre seat post for you. There is some evidence here to support those two claims.

Fredo76

Every single broken carbon seatpost anecdote is a perfectly fine argument against their use, all by itself. Especially so when compared to the relative lack of broken non-carbon seatpost anecdotes.

genejockey 

Ahem.

Eric F

This thread includes anecdotal evidence of broken non-carbon seatposts as well. One could conclude that neither CF, nor aluminum, are good materials for seatposts.

wolfchild

I have aluminum seat posts on all 3 of my bikes and never experienced any of the problems you just mentioned.

Fredo76

Those are all good arguments against extra-light aluminum seatposts, I assume.

I want a seatpost that won't break. They didn't used to break, iirc.

Luckily, all of mine qualify.

Eric F

This doesn't mean that it's not a possibility for other people. In exactly the same way, I have 6 CF seatposts on my current bikes that have never had problems, including some that are 20+ years old. Yet, despite my success, other people have had failures, for various reasons.